1. Field of the Invention
The present invention relates generally to radar imaging, and more particularly to high resolution radar imaging using a sparse array of time modulated ultra wideband radars.
2. Related Art
Many applications today would benefit from high resolution radar imaging. For instance, law enforcement agencies often are confronted with hostage situations where armed intruders are barricaded inside a building. Officers on the scene generally have no means for determining the number and position of persons within the building, and are thus hampered in their efforts to resolve the situation. Similarly, law enforcement personnel planning a surprise raid on an armed compound would also greatly benefit from information related to the number and position of persons within. An imaging system that could be deployed in a covert manner outside the building for imaging personnel inside the building would therefore be of great assistance to law enforcement agencies.
Various motion sensing applications would also benefit from high resolution radar data. One example would be a motion sensor that is required to detect motion in a narrow hallway from a distant point in the building, while ignoring motion in the rooms adjacent to the hallway. Another example would be a home security motion sensor designed to detect intruders entering the house but to ignore movement within. Other examples include applications which require a combination of radar imaging and motion sensing. These combined imaging/motion sensing systems could be used to distinguish moving targets from stationary targets, or to provide an image of the building structure with a superimposed image showing the location of moving objects. Even more sophisticated systems could identify various targets based on specific movements, such as vital signs.
Conventional narrowband imaging devices are unable to provide this type of functionality. The applications described above require that the system be able to resolve closely spaced objects at a distance, inside a building. In order to achieve the necessary angular resolution, the pulses of electromagnetic radiation used to image the building must either be transmitted from multiple radiators (whether multiple antennas attached to a single source, or multiple sources) spaced wide distances apart, or the frequency of the transmitted radiation must be increased.
Neither approach is adequate. The spacing between radiating elements required to achieve the necessary resolution greatly exceeds one quarter of the operating wavelength (i.e., a sparse array) and therefore suffers from off-axis ambiguities. The resolution might be increased by increasing the operating frequency, but in doing so, decreases penetration and increases scattering. Narrowband pulses having sufficiently high frequency for the required resolution would be unable to penetrate a building. As a result, conventional narrowband systems cannot provide the functionality described for the above applications.
A need therefore exists for an improved system and method for high resolution, building penetrating, radar imaging.